(1) Field of the Invention
The present invention relates to an optical disk apparatus that records information on or reads information out of an optical disk, and more particularly to an optical disk apparatus that highly accurately performs tracking control when recording or reading information in particular.
(2) Description of the Related Arts
The stability of tracking servo control is important for the reliability of an optical disk apparatus. The stability of tracking servo control is mainly determined by the stability of signals that the zero point of a tracking error signal is correctly matched with the center of a record information track under various use conditions, and a shift from the zero point is referred to as the offset of the tracking error signal.
Ideally, the offset of the tracking error signal is close to zero without limit (there is no shift). However, a shift occurs due to manufacture variations in a pickup that is an optical head and variations in media such as the eccentricity, warpage, and waviness of a disk to cause an offset. The zero point of a signal is sifted to disable correct servo control on the center of a track, causing a pickup to go out of a track in recording and reading a disk.
For measures to improve this problem, methods for correcting an offset that is a shift value in processing signals are described in Japanese Patent Application Laid-Open Publication No. 2006-294189 and Japanese Patent Application Laid-Open Publication No. 2011-065702.
In Japanese Patent Application Laid-Open Publication No. 2006-294189, an object is to highly accurately correct the offset of a tracking error signal even in the case where there are nonlinear characteristics such as a shift value between the position of an objective lens and the mechanical neutral position of the objective lens being not proportional to the offset value of the tracking error signal, and such a confutation is provided in which the shift value between the objective lens position and the mechanical neutral position of the objective lens is estimated and any one of a plurality of correcting functions is used according to the estimated shift value of the objective lens position to generate a correcting signal for the tracking error signal.
Moreover, in Japanese Patent Application Laid-Open Publication No. 2011-065702, an object is to correct the nonlinear offset of a tracking error signal, and there is disclosed that a drive circuit learns and corrects the non-linearity of the offset of a differential push-pull signal in association with a lens shift, in which the drive circuit measures an offset curve by learning and stores a correcting value, and in servo control, the correcting value is used to correct the tracking error signal for correcting a nonlinear component.